1. Field of the Invention
This invention relates to an apparatus for a method of RF amplification of signals up to 1 GHz for CATV repeater stations. Presently available 77 channel CATV RF distribution systems may be converted to 151 channel distribution systems by installing the gain stage of the present invention in place of gain stages utilized in systems up to 550 MHz. The present invention provides a gain stage which is pin for pin compatible with existing gain stages.
2. Description of the Prior Art
Presently available CATV equipment utilizes a frequency spectrum ranging from 50 MHz to 550 MHz. This frequency range enables commercial CATV operators to deliver 77 channels over coaxial networks to cable subscribers. A one GHz CATV amplifier will provide a broader frequency spectrum, enabling CATV transmission of 151 channels over the same systems which are currently delivering 77 channels.
At frequencies above 550 MHz, problems are encountered in the design of circuits because as the frequency increases the size of the components must decrease. The miniaturization of electromagnetic components such as inductors and impedance matching transformers presents a difficult design hurdle. Second harmonic distortion traditionally has been eliminated by means of push-pull amplification. This cancellation process developed first in audio equipment. It is relatively easy to achieve a phase shift of 180.degree. at frequencies below 20 MHz. This is adequate for design purposes in the audio ranges and up to 20 MHz. CATV industry has developed transmissions up to 550 MHz. However, attempts to design a circuit which approaches 180.degree. phase shift at transmission frequencies exceeding 550 MHz, have been unsuccessful. It is desirable though to approach 180.degree. as nearly as possible, which ideally will cancel all distortion due to second and third harmonics and multiples thereof These harmonics are commonly referred to as "2IM" and Composite Triple Beat (CTB). This provides optimal linearity between the input and the output signal of the amplifier.